1. Field of the Invention
The present invention relates to an electrophotographic copying machine having an automatic paper selecting function and particularly to an electrophotographic copying machine having an improved efficiency of operation in an automatic paper selection mode.
2. Description of the Prior Art
In the prior art, there is known an electrophotographic copying machine having an automatic paper selection mode, which comprises a plurality of paper feed portions for containing paper of different sizes and which automatically selects a paper feed portion containing paper of a size corresponding to a size of a document to be copied, thereby to perform a copy operation using the paper in the selected paper feed portion.
In such an electrophotographic copying machine, if the automatic paper selection mode is selected and a print key is pressed, the size of the document is detected and then a paper feed portion containing paper suited for the detected size of the document is automatically selected, whereby the copy operation is performed.
Such an automatic paper selection mode is disclosed for example in the below indicated documents.
The U.S. Pat. No. 3,684,373 discloses a technique in which a size of a document fed is detected by a switch and paper suited for the detected size is used for a copy operation; the U.S. Pat. No. 3,689,143 discloses a technique in which a size of a document fed is detected by sensors and a paper feed portion containing paper suited for the detected size and a magnification are selected; the U.S. Pat. No. 4,455,081 discloses a technique in which a size of a document fed is detected by switches and a paper feed portion containing paper suited for the detected size is selected; and "COPY SIZE SELECTION" by J. L. Bacon in IBM Technical Disclosure Bulletin Vol. 17 No. 9, February 1975, pp. 2690-2690A discloses a technique in which a size of a document fed is detected by a sensor and clocks and a paper feed portion containing paper suited for the detected size is selected for copy operation.
There is known another technique in which a magnification is automatically adjusted by evaluatnng the optimum magnification based on a size of a document and a size of copy paper, which is disclosed for example in the U.S. Pat. No. 4,277,163.
Generally in an electrophotographic copying machine, if paper does not exist in a selected paper feed portion, control is effected to forbid input by a print key irrespective of whether an automatic paper selection mode is adopted or not. For example, the U.S. Pat. No. 4,108,427 discloses that if paper does not exist in a selected paper feed portion, copy operation is forbidden to cause a display device to indicate the need for supply of paper.
Consequently, in a copying machine having such an automatic paper selection mode, input by a print key is forbidden when paper does not exist in a presently selected paper feed portion and, as a result, a copy operation can not be started even if paper of a suitable size is contained in other paper feed portions, which considerably reduces efficiency in copy operation.